The invention relates to a balanced-pressure multi-compartment vessel for a thermodynamic energy converter, the thermodynamic energy converter and a method for operating the thermodynamic energy converter. The energy converter serves to convert thermal energy into mechanical energy and mechanical energy into thermal energy, respectively. In a thermodynamic cycle, a gaseous working medium is heated from the outside through supply of higher-temperature heat energy and cooled from the outside in a cyclical sequence through removal with lower-temperature heat energy. The mechanical energy is generated through expansion work. The initial state is reached after completion of one cycle. A so-called balanced-pressure multi-compartment vessel is a volume element for enclosing a working medium which comprises multiple compartments between which the pressure of the working medium will always balance itself out.
A crucial aspect of a cycle is that after completion of one such cycle the working means assumes the same state it had at the beginning of the cycle. If a gas is used as the working medium, its state is defined by the three state parameters p (pressure), V (volume) and T (temperature). Assuming an ideal gas, the relationship between these parameters is as follows:
            p      ×      V        T    =      const    .  
If one follows this basic principle of thermodynamics and uses it as a basis for constructing a working or thermal engine, all that is required is a component which is capable of selectively keeping constant or changing the state parameters p, V and T individually or in combination. With this component, it is then possible to implement individual changes of the state of a working means (e.g. isochoric, isothermal, isobaric, adiabatic or polytropic change of state) in an optimal manner. As a consequence, it becomes possible to technically implement any desired cycle solely through a sequence of different changes of the state of the working means using this single component.
The cycle may take place in a thermal engine that is equipped with cylinders and pistons and in which the expansion work is converted into mechanical energy via rotary motion of moving mechanical pistons, the connecting rod and the crankshaft. Such a thermal engine is described in U.S. Pat. No. 8,938,942 B2. Said document provides an external-combustion, closed-cycle thermal engine. Said engine includes a gas chamber, a heater and a cooler, which are closed. Flow paths connect the gas chamber and the respective inlet and outlet sides of the heater and the cooler, which can be opened or closed through on-off valves. Further, a means is provided for moving a working gas. The switching of the supply of the working gas between the heater and the cooler occurs through on-off valves. A working device, particularly a cylinder with a piston and a crankshaft drive, is provided which is driven by the contracting and expanding working gas. The volume of the heater or the cooler does not affect the efficiency of the engine, and the engine operates under various conditions.
Such known systems for the conversion of thermal energy into mechanical energy and mechanical energy into thermal energy, respectively, in each case follow a single, fixed cycle. This is disadvantageous in that, in the respective fields of operation, the scope of operation of the design is limited in this respect. However, constrictions are primarily caused by the rigid movement patterns dictated by the crankshaft drive.
Another energy converter for the conversion of thermal energy into mechanical energy is known from EP 2 775 109 A1. The disclosure of this document likewise utilizes the effect that with the aid of a single change of state, work can be gained from a certain amount of gaseous working medium only once. In order to repeat the power gain, the working means needs to be returned to the initial state. A simple reversal of the change of state, assuming complete reversibility, will in both cases just consume the previously gained work. If work is to be gained, the initial state needs to be reached through different ways. In this case, the state changes cyclically, i.e., the working means passes through a cycle. Only then can heat be converted into work constantly. The gaseous working medium is located in a volume that is closed to the outside.
The two pressure vessels, which are partially filled with hydraulic oil as a displacement fluid, are hydraulically coupled to valves via a pipeline network. If expansion work of the working medium in the first pressure vessel causes a cover surface of the displacement fluid to move in one direction, e.g. downward, and the displacement fluid to move from the first to the second pressure vessel, the cover surface of the displacement fluid of the second pressure vessel, which is complementary to the first one, will move in the opposite direction. Integrated in the pipeline network between the two pressure vessels is a force-transforming unit, e.g. a hydraulic motor or a linear drive, through which mechanical energy can be utilized. Due to the two hydraulically connected pressure vessels, two simultaneous cycles take place, although with a stroke-shifted sequence of the changes of state.
The geometrical constriction of the process sequence caused by the movement patterns dictated by the crankshaft drive are overcome here since the force transmission of the expansion work is not effected through the mechanical piston in the cylinder but through a practically incompressible hydraulic liquid such as hydraulic oil. The hydraulic oil at the same time provides for force transmission via a pipeline, e.g. to a hydraulic motor which transforms the mechanical energy into a rotary motion and thus utilizes it.
Due to the design providing for regulation with the aid of the valves and the speed of the tube fans proposed in the prior art, various polytropic compression paths and expansion paths of the working medium are possible. These are limited, however, by their regulation and by the volume of the space in the pressure vessel.